The present invention relates to magnetic bearing devices comprising a plurality of magnetic bearings for contactlessly supporting a rotary body axially and radially thereof, and a method of starting the device.
Already known as such magnetic bearing devices are those comprising a magnetic bearing main body and a controller connected to the main body by a cable. The main body includes a plurality of magnetic bearings for magnetically levitating the rotary body, a plurality of position sensors for detecting the position of the rotary body with respect to the axial and radial directions, and a plurality of protective bearings for limiting the movable range of the rotary body. Each of the magnetic bearings comprises one or two pairs of opposed electromagnets arranged on opposite sides of an axial or radial control axis. The protective bearings restrict the movable range of the rotary body with respect to the axial and radial directions and mechanically support the rotary body when the magnetic bearings produce no magnetic levitation force. The controller controls the electromagnets of the magnetic bearings according to the output signals of the position sensors.
With such magnetic bearing devices, variations occur in mechanical accuracy and in physical characteristics. The variations in mechanical accuracy are attributable to mechanical errors involved in the manufacturing or assembling process. Predominant among the mechanical errors is the difference between the position of the center of the rotary body relative to the electromagnets (magnetic center position) and the position of the center of the rotary body relative to the protective bearings (mechanical center position). Although the magnetic bearing device is so designed that the magnetic center position matches the mechanical center position, an error will occur in these positions relative to each other owing to manufacturing or assembling errors. Furthermore, manufacturing or assembling errors are likely to result in variations in physical characteristics such as the characteristic frequency of the rotary body and unbalance.
In operating the magnetic bearing device, it is desired that the rotary body be held in the magnetic center position because if the-rotary body is magnetically out of alignment, a linear relationship will not be established between the exciting current supplied to the pair of electromagnets of the magnetic bearing and the force of magnetic attraction produced by the pair of electromagnets to entail unstable control. Conventionally, therefore, it is practice to adjust the controller at the installation site of the magnetic bearing device by magnetically levitating the rotary body so as to hold the levitated rotary body in the magnetic center position. It is relatively easy to hold the rotary body in the mechanical center position, whereas in order to hold the rotary body in the magnetic center position, the error in the magnetic center position relative to the mechanical center position must be eliminated by adjusting the controller. The control parameters of the controller need also to be adjusted and are therefore adjusted at the same time in order to correct the characteristic frequency and unbalance of the rotary body.
Since the mechanical accuracy and physical characteristics of the magnetic bearing device differ from device to device, the adjustment of the controller is required for all magnetic bearing devices. The adjustment of the controller moreover requires special knowledge and a cumbersome procedure, which must be performed at the installation site of the user by the special technician of the manufacturer. The device therefore has the problem that the adjustment of the controller is time-consuming and costly.
To simplify the adjustment of the controller, it appears feasible to render the controller less sophisticated in performance, with some variations in mechanical accuracy and physical characteristics taken into consideration, whereas the magnetic bearing device will then become less efficient in performance to an undesirable extent.
An object of the present invention is to overcome the foregoing problems and to provide a magnetic bearing device and a method of starting the device, the device having a controller which is made easy to adjust for correcting variations in mechanical accuracy and physical characteristics without impairing the performance of the device to an undesirable extent.
The present invention provides a magnetic bearing device comprising a magnetic bearing main body having at least electromagnets for magnetically levitating a rotary body and position sensors for detecting the position of the rotary body, and a controller connected to the main body by a cable for controlling the electromagnets based on output signals of the position sensors, the device being characterized in that the magnetic bearing main body is provided with memory means having stored therein characteristics of the rotary body and the electromagnets.
Since the magnetic bearing main body is provided with the memory means having stored therein various characteristics of the rotary body and the electromagnets, the mechanical accuracy and physical characteristics of the bearing device can be recognized by reading the information in the memory means with the controller when the controller is connected to the magnetic bearing main body. The controller is then adjustable by a simple procedure with reference to the information, so that there is no need to perform a cumbersome adjusting procedure by levitating the rotary body at the site of installation. Even the user having no special knowledge can therefore adjust the controller. This makes it no longer necessary for the manufacturer to dispatch the special technician for the adjustment, consequently reducing the adjusting time and expense. Moreover, it is unlikely that the overall performance of the magnetic bearing device will become impaired more than is necessary since each device is adjustable based on the characteristics thereof.
Preferably, the controller is provided with read means for reading information from the memory means of the magnetic bearing main body, and means for setting control parameters based on the information.
The controller is then adjustable automatically and more easily.
The present invention provides a method of starting a magnetic bearing device comprising a magnetic bearing main body having at least electromagnets for magnetically levitating a rotary body and position sensors for detecting the position of the rotary body, and a controller connected to the main body by a cable for controlling the electromagnets based on output signals of the position sensors, the magnetic bearing main body being provided with memory means having stored therein characteristics of the rotary body and the electromagnets, the controller being provided with read means for reading information from the memory means of the main body, and means for setting control parameters based on the information, the method being characterized by reading the information from the memory means of the main body with the read means of the controller, and setting control parameters by the setting means of the controller based on the information to start the magnetic bearing device.
For starting the device, the controller is adjustable automatically with extreme ease by the method of the invention.